1. Field of the Invention
The present invention relates in general to a method for writing data to an optical disc, and in particular to a method using different data writing strategies according to the rotation speed of the disc drive.
2. Description of the Related Art
CDRW (ReWritable) drivers are designed to record data, video and other content from PC and other platforms. CDRW main factures recognize that content must be portable across various platforms.
The recording layer of a blank CDRW disc is polycrystalline, which is a phase-change material. During writing, a focused laser beam selectively heats partial areas of the phase-change material to be above the melting temperature of 500-700° C., so all the atoms in this area can move rapidly in the liquid state causing by the high temperature. When cooled with sufficiently quickly, the random liquid state is ‘frozen-in’ and the so-called amorphous state is obtained. If the phase-change layer is heated to below the melting temperature but above the crystallization temperature (200° C.) for a sufficient time (at least longer than the minimum crystallization time), the atoms revert back to an ordered state, i.e. the crystalline state.
The amorphous and crystalline states have different refractive indexes, and can therefore be optically distinguished. For a CDRW disc, the amorphous state has a lower reflectivity than in the crystalline state and, during read-out, this produces a signal identical to that of a regular dual layer CDRW disc, making it possible to read CDRW discs with CD-ROM drives and CD Video players.
The phase-change medium can be rewritten in a single pass of the focused laser beam. In the CDRW system, the data is recorded on discs by means of a write strategy, using different laser output levels. This strategy has two parts, a pulsed part (pulsing is necessary to write amorphous ‘marks’), and a non-pulsed part, in which the strategy writes crystalline areas between the marks.
The write strategy is determined according to the type of optical disc, and the CDRW drive, and the recording speed. FIG. 1 shows a power waveform of one write strategy. In FIG. 1, the laser modulation strategy records the shortest ‘pit’ defined in the CD system, the ‘3T mark’, and the write strategy to record ‘no mark’. Recording a mark means creating a low-reflectivity (amorphous) region in the active layer, and recording no mark means creating a high-reflectivity (polycrystalline) region.
Different write strategies are implemented according to different predetermined ranges of optical data recording speed. For example, a first write strategy is used for recording data speed under 16×. Here, the pulse width of the first write strategy is adjustable to meet different data recording speeds under 16×. While the data recording speed exceeds 16×, the first write strategy does not conform to the data recording speed by adjusting the pulse width of the same write strategy. Thus, the recorded mark fails. Therefore, another write strategy is employed record data at a speed exceeding 16×.
The data recording speed of CDRW drive, however, may be determined according to the quality of the optical disc or performance of the host computer. In addition, in CAV (constant angular velocity) mode, the data recording speed is altered according to different recording radius of the optical disc. Moreover, the new data recording speed may correspond to a different write strategy. Thus, the conventional optical data recording method limits the recording speed to prevent the problems mentioned above.